Journal of Power Sources 125 (2004) 256–266
Electrolytic MnO
2
via non-isothermal electrode heating: a promising
approach for optimizing performances of electroactive materials
M. Ghaemi
∗
, R.K. Ghavami, L. Khosravi-Fard, M.Z. Kassaee
Department of Chemistry, School of Sciences, Tarbiat Modarres University, P.O. Box 14115-175, Tehran, Iran
Received 14 July 2003; accepted 28 July 2003
Abstract
A thermal-modulated electrodeposition technique is proposed for enhancing the physico-chemical characteristics of electrolytic man-
ganese dioxide (EMD). Synthesis is conducted on the basis of non-isothermal electrode heating at ambient pressure. Electrode substrates
are heated continuously during the anodic deposition processes in boiling sulfuric acid solutions. Bath temperatures and deposition pa-
rameters are held constant. Anode temperatures are varied in the range 98–150
◦
C. Two series of products, one deposited on a lead and the
other on a Ti cylinder, are investigated. These are compared with EMD prepared by the conventional isothermal method which is similarly
produced in a boiling solution. At optimized anode temperatures (120–135
◦
C), both series of products display enhanced charge–discharge
performance. This is consistent with the compact surface morphologies which are obtained for thin layers of EMD deposited on graphite
substrates.
The positive effects of localized heating are detected by electrochemical impedance spectroscopy. Several physico-chemical parameters
of the solvent, as well as of the electrodes, are varied as a function of electrode temperatures. Conservation of energy can be obtained
through a relatively safe, simple and low-cost process. This method has potential for application to other electroactive materials with
industrial prospects.
© 2003 Elsevier B.V. All rights reserved.
Keywords: Non-isothermal electrodeposition; Electrode heating; Electrolytic manganese dioxide; Rechargeable alkaline manganese batteries
1. Introduction
Optimization of manufacturing parameters is of consid-
erable interest for the development of advanced battery
materials of high specific energy [1,2]. In this respect, many
attempt have been made to lower energy consumption and
processing cost by employing more efficient and innova-
tive methods of synthesis. Many electrochemical aqueous
systems suffer the disadvantage of not being able to be re-
duced or oxidized at temperatures below the boiling point
of water. Nevertheless, several new radiation and thermal
methods for the activation of electrochemical processes
have emerged [3–7]. The ultimate solution appears to lie in
finding a route to concentrate the thermal energy at the re-
action surfaces. Perhaps the most favorable approach would
be to concentrate the heat, in the thin hot solution layer,
near the electrode surface [8]; as opposed to warming up
the entire cell volume. While the idea may not be new, its
∗
Corresponding author. Tel.: +98-21-801-1001/3417;
fax: +98-21-800-9730.
E-mail address: ghaemi
m@modares.ac.ir (M. Ghaemi).
principles have rarely been employed in electrosynthesis.
The localized heating technique originally started with the
pioneering work of Gründler et al. [9,10] who employed a
contact technique called ‘hot-wire electrochemistry’. This
involves simultaneous heating of the working electrode with
both alternating current and direct current. Such a tech-
nique allows a higher energy density to be localized in a
small spot, near the working electrode. This activates those
electrochemical processes which have slow charge-transfer
kinetics at the lower temperature of the bulk solution. In ad-
dition, electrodeposition can be performed rapidly without
waiting for warming up of the entire electrolyte solution.
This saves both energy and time. Non-contact techniques
with external heating (focused laser beam, microwave
radiation, ultrasound, etc.) can also be used to heat elec-
trode/electrolyte interfaces that have complex shapes [3,11].
The reaction zone may be heated to more than 373 K in
an aqueous solution at atmospheric pressure and this may
modify the electrocrystallization process [12].
A directly-heated electrode can be used to enhance the
properties of electroactive materials, in particular those
of semiconductors [13]. In this way, a stationary temper-
0378-7753/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jpowsour.2003.08.036